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Lithops have a small vocabulary of failures, and the good news is that they look quite different from one another. Before treating anything, look at the whole plant: the top surface, the flanks, the neck where the body meets the mix, and if you have any doubt, the roots. Most of the time the answer is that a watering happened in the wrong phase of the cycle, and the treatment is to stop rather than to add something.
| What you see | Most likely cause | What to do |
|---|---|---|
| Split down the flank, edges gaping | Watered while the new pair was forming | Stop watering, keep dry and airy, let it heal to a scar |
| Two pairs stacked, old pair still fat | Watered through the leaf change | Withhold all water until the old pair is paper |
| Body soft, base brown or black | Rot at the neck or root | Unpot the same day and cut back to clean tissue |
| Pale, elongated, rising out of the grit | Not enough light | Move to full sun over two to three weeks; damage is permanent |
| White bleached patch on the shoulder | Sudden increase in sun | Shade for a fortnight, then reintroduce sun gradually |
| White cottony specks in the slit or on roots | Mealybug or root mealybug | Isolate and treat; check every other plant nearby |
| Fine webbing and stippled dull surface | Spider mite | Raise humidity briefly, treat, improve air movement |
| Small flies over the surface | Fungus gnats, meaning the mix is too wet | Let the pot dry right out; fix the mix at the next repot |
Splitting and bursting, the signature injury
A lithops that has been watered during the leaf change takes up water it cannot use. The new pair swells against skin that has not had time to expand, and the plant splits along the side, sometimes with a visible wound that weeps. It can also throw a second pair of leaves while the first is still fully turgid, so you end up with a stacked, misshapen plant carrying four leaves instead of two.
Neither is fatal on its own. A clean split dries into a corky brown scar within a couple of weeks if the plant is kept completely dry and in good air movement, and that scar disappears at the next leaf change when the damaged pair is absorbed. The real danger is that an open wound plus moisture equals rot, so the treatment is aggressive dryness rather than any product. Keep the pot dry, keep water off the body entirely, and give the plant as much sun and airflow as you have.
A stacked plant needs the same discipline for longer. Withhold water completely until every one of the old leaves has gone to paper, which may take an extra couple of months, then resume the normal cycle. Plants usually sort themselves out within one full cycle, though a badly stacked specimen can look wrong for two years.
Resist the urge to peel off the old leaves to tidy a stacked or splitting plant. Pulling them tears the new pair beneath and leaves a wound where the plant is least able to defend itself. The old leaves must be allowed to dry down on their own.
Rot: the only emergency
Rot moves fast and it is the one problem where the correct response is the same day, not the weekend. It starts at the neck or in the roots, usually after water sat in the mix during a cool spell or during the leaf change, and it shows as a soft, discolored, sometimes translucent zone that spreads upward. Pressed gently, an affected body gives like a grape.
- Unpot immediately and inspect Tip the plant out and clear the grit from the roots. Look for black, hollow or mushy root sections and for browning at the neck. If the rot has already reached the middle of the body, the plant is lost and the priority becomes protecting the pots next to it.
- Cut back to clean tissue With a blade wiped clean between cuts, remove every affected root and any browned tissue at the base. Keep cutting until the exposed surface is uniformly pale and firm. Rot left behind will simply resume.
- Dry the plant in open air Leave it out of any pot for five to seven days somewhere bright, airy and out of direct sun, so the cut surfaces callus completely. This is not optional; potting a wet cut straight back into mix restarts the problem.
- Repot dry and wait Pot into fresh, sharply drained mix and give no water for at least two weeks, longer if the plant lost most of its roots. New roots often form before you see anything above ground, and the first sign of success is the body firming up after the first cautious watering.
Pests, and the two that hide
Lithops attract fewer pests than most succulents, largely because there is so little plant to attack, but the ones that do arrive tend to hide in places you cannot see without looking deliberately. Check the slit between the leaves and the surface of the roots every time you repot, and once a month during growing season for anything you keep near other plants.
| Pest | Where it hides | How to deal with it |
|---|---|---|
| Mealybug | Deep in the slit and under the shoulders | Touch each insect with a cotton bud dipped in rubbing alcohol, repeat weekly for a month |
| Root mealybug | On the roots, as white powder and cotton | Bare-root the plant, wash the roots, discard the old mix and pot, treat before repotting |
| Spider mite | On the top surface, in dry still air | Wipe the body, improve air movement, treat with a miticide or soap solution |
| Scale | On the flanks near the mix line | Scrape off with a fingernail and treat with alcohol as for mealybug |
| Fungus gnats | In damp organic material at the surface | Not damaging in themselves; treat as a signal that the mix is holding too much water |
| Slugs and rodents outdoors | Under the pot rim and around the grit | Bring pots up off the ground, use a physical barrier, check after rain |
Damage from light, and the record that stops it happening twice
Etiolation is worth naming as a problem rather than a preference, because it is the most common way a lithops is lost slowly. A stretched plant is weaker, less able to store water, and eventually falls over and rots at the point of contact with the grit. It cannot be reversed. What you can do is fix the light immediately so that the next leaf pair forms correctly, and accept that the current body will stay stretched until it is absorbed.
Sunburn is the opposite error and shows as a bleached or brown dry patch that appears within a day or two of a change in exposure. It never spreads and never softens, which is how you distinguish it from rot. It disfigures the plant for the life of that leaf pair and no more.
Keep a simple problem log with three columns: the date, what you saw, and what had changed in the previous two weeks. Almost every entry will resolve to a watering, a move, or a warm damp spell, and after one season the pattern is obvious enough that you can predict the trouble instead of diagnosing it. Note in particular the date of the last watering before any problem appeared, because with lithops that one number usually contains the whole explanation.
When a plant is in trouble and you are unsure what is wrong, the safe default is always more light, more air and no water. There is no lithops problem that is made worse by those three things, and several that are cured by them alone.